'You Kick Like A Girl': New Study Finds Men and Women Use Different Leg and Hip Muscles During...

Forbes.com—September 1, 2010

May Help Explain Higher Risk of ACL Injury in Females; Improve Prevention Approach

Significant differences in knee alignment and muscle activation exist between men and women while kicking a soccer ball, according to a study published this month in the Journal of Bone and Joint Surgery. Data reveals that males activate certain hip and leg muscles more than females during the motion of the instep and side-foot kicks - the most common soccer kicks - which may help explain why female players are more than twice as likely as males to sustain an Anterior Cruciate Ligament (ACL) injury.

Soccer is one of the fastest-growing sports in the United States with approximately 20 million registered players* and an annual participation increase of more than 20 percent(1), according to statistics from the National Collegiate Athletic Association (NCAA)(2). Women also are playing this sport on more competitive levels. Prior research shows that females are more prone to non-contact ACL injuries than males and though many theories exist, a direct cause for the disparity is unknown.

"By analyzing the detailed motion of a soccer kick in progress, our goal was to home in on some of the differences between the sexes and how they may relate to injury risk," said orthopaedic surgeon Robert H. Brophy, M.D., study author who was formerly a sports medicine fellow at Hospital for Special Surgery and is now assistant professor of orthopedics, Washington University School of Medicine in St. Louis. "This study offers more information to help us better understand the differences between male and female athletes, particularly soccer players."

Dr. Brophy and his colleagues from the Motion Analysis Laboratory and Sports Medicine Service at Hospital for Special Surgery in New York used 3-D video-based motion analysis and electromyography to examine the differences between 13 male and 12 female college soccer players during the action of kicking a soccer ball.

Using eight to 10 video cameras, 21 retroreflective markers and 16 electrodes simultaneously, researchers measured the activation of seven muscles (iliacus, gluteus maximus, gluteus medius, vastus lateralis, vastus medialis, hamstrings and gastrocnemius) in both the kicking and supporting legs; as well as two additional muscles (hip adductors and tibialis anterior) in the kicking leg only. Five instep and five side-foot kicks were recorded for each player. Muscle activation was recorded as a percentage of maximum voluntary isometric contraction.

They found that male players activate the hip flexors (inside of the hip) in their kicking leg and the hip abductors (outside of the hip) in their supporting leg more than females.